Practical MR physics: and case file of MR artifacts and pitfalls

315 Pages·2010·7.44 MB·English

by  Alexander C. Mamourian

PRACTICAL MR PHYSICS
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PRACTICAL MR PHYSICS
AND CASE FILE OF MR ARTIFACTS
AND PITFALLS
Alexander C. Mamourian, MD
Associate Professor of Radiology
Division of Neuroradiology
University of Pennsylvania
Philadelphia, Pennsylvania
1
2010
3
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Copyright © 2010 by Oxford University Press, Inc.
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First published 2010
All rights reserved. No part of this publication may be reproduced,
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Library of Congress Cataloging-in-Publication Data
Mamourian, Alexander C.
Practical MR physics: And case fi le of MR artifacts and pitfalls / Alexander C. Mamourian.
p. ; cm.
Includes bibliographical references and index.
ISBN 978–0–19–537281–6
1. Medical physics. 2. Magnetic resonance imaging. 3. Nuclear magnetic resonance.
I. Title. [DNLM: 1. Magnetic Resonance Imaging—Case Reports. 2. Magnetic Resonance
Imaging—Problems and Exercises. 3. Image Interpretation, Computer-Assisted—Case Reports.
4. Image Interpretation, Computer-Assisted—Problems and Exercises. WN 18.2 M265p 2010]
R895.M26 2010
616.07’548—dc22
2009030871
All photographs by Alexander C. Mamourian.
1 3 5 7 9 8 6 4 2
Printed in the United States of America
on acid-free paper
CONTENTS
Preface vii
Acknowledgments ix
1 MR PHYSICS 1
2 MR ARTIFACTS 45
3 MR PITFALLS 167
4 TEN PUZZLERS 275
Index 301
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PREFACE
When I fi lled out my application for a fellowship in MR imaging at the University of Pennsylvania
25 years ago, I was required to write an essay. I included in mine, at the urging of my sister Alicia, a
plan to write a book about MR physics. I was never sure of whether it was because of, or in spite of,
that essay the department chairman, Dr. Stanley Baum, accepted me for the fellowship but told me
during my interview that this was among the most naive ideas he had ever heard from a prospective
fellow. There was some truth to that since I was one year out of my residency training. It seems like
a better idea now.
While MR physics has never been an easy subject to master, the bar is higher than ever since MR
imaging techniques have become more complex. I suspect that many trainees have given up altogether
and treat MR with due respect but at arms length, much as I treat my car’s engine. Still, it is helpful to
have some understanding of MR physics so that you can suggest ways to improve image quality and
avoid mistaking common artifacts for disease.
I am not a physicist; this will prove to be a good thing for some readers and disappointing for others.
Magnetic resonance imaging has been my professional focus for many years, however, and I hope you
will fi nd the explanations and analogies drawn from that experience clear and helpful. This book is
not intended to replace the many fi ne books that focus on MR physics. While the basics of MR physics
are included in Chapter 1, my goal is to use case material to illustrate how those principles will help
you to identify and understand common artifacts. After reading this book, you will be better prepared
to understand more advanced MR techniques as well.
The book is divided into four parts: (1) an overview of MR physics, (2) common MR artifacts,
(3) common MR pitfalls, and (4) challenging cases. There are several ways you can use the book. For
most readers who want to learn more about MR imaging, cover to cover will do best. You will also
fi nd in the book links to fi ve instructional videos on the web that were created to complement this
text. I encourage you to view them since the selected topics, such as the motion of precession, are eas-
ier to demonstrate than explain. If you are comfortable with the physics, a review of the artifacts and
pitfalls should sharpen your imaging skills and will provide a refresher on MR physics. The answer
for each case will be defi ned by a box, usually at the bottom of the page, so avert your gaze until you
are ready for it. If you are an experienced imager but happen to encounter what you think is an arti-
fact while you are reviewing clinical MR images, you can use the index in this book to investigate that
topic. All readers should try to solve the puzzler cases either before or after reading the book, but the
answers will surely come more easily afterward. It is my hope that this book proves to be valuable to
you and, in that way, helpful to your patients.
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ACKNOWLEDGMENTS
I am grateful for the time with my grandfather Garabed, who provided the groundwork; my parents,
Marcus and Maritza, for helping me fi nd my way; my sister Alicia, especially for drafting that essay;
and my children, Ani, Molly, Liz, and Marcus, for giving me all the joyful reasons. To my wife Pam,
words cannot express the depth of my gratitude for surely without you this book would have remained
an unfulfi lled promise.
I also want to thank the many gifted MR technologists I have worked with over the years, with
special thanks to Swapan Sen, Chris Harris, Sharon Hurst, Bob Ferranti, Shreve Soule, and Theresa
Haron, Theresa for both her competence and her keen eye.
My sincere thanks go to Andrea Seils at Oxford University Press for believing in this project, Josef
Debbins, PhD, at the Barrow Institute, for keeping me true to the facts and guiding me to a better
understanding of phase encoding, and to Doug Goodwin, MD, at Dartmouth-Hitchcock Medical
Center for providing these exquisite musculoskeletal cases.
Finally, my eternal gratitude to Dr. Robert Spetzler and the NICU nursing staff at the Barrow
Institute for giving me a second chance and inspiring me to write this book.